Tread ring for removable tread tires

ABSTRACT

A separable tread ring for pneumatic tires which embodies an armor longitudinally resistant to tension, the armor being formed by a helically wound metal cord, the coils of which are disposed generally parallel to the mid-circumferential plane of the tire. Two additional layers of metal cords parallel to each other in each layer are provided, the cords being disposed in two directions crossed relative to the mid-circumferential plane at angles ranging from 10* to 65*. The latter layers are disposed radially inwardly relative to the armor. A third layer of extensible metal cords is positioned radially outwardly of the armor, the cords of such layer being inclined with respect to the mid-circumferential plane at an angle ranging between 10* and 65*.

United States Patent Lugli 152 361 Magistrini et aL 1 51 June 6, 1972541 TREAD RING FOR REMOVABLE 3,503,432 3/1970 Maiocchi 152/176 TREADTIRES 1,689,119 10/1928 Evans 152/359 [72] Inventors: Carlo Magistrini,Monza; Luigi Maiocchi, FOREIGN PATENTS OR APPLICATIONS M'l b t f It haly 1,395,033 3/1965 France 152/361 [73] Assignee: Industrie PirelliS.p.A., Milan, Italy Primary Examiner-Arthur L. La Point [22] Flled'June 1970 AttorneyStevens, Davis, Miller & Mosher [2]] Appl. No.: 51,100

v 57] ABSTRACT [30] Foreign Application Priority Data A se arable treadring for pneumatic tires which embodies an p l d ll h b armor ongitu inay resistant to tension, t e armor eing a formed by a helically woundmetal cord, the coils of which'are a y 1 disposed generally parallel tothe mid-circumferential plane of I the tire. Two additional layers ofmetalcords parallel to each 52 us. 01 .,l52/l76, 161/58, 1165120114847,(her in each layer are provided, the cords being disposed in l 5 I] IntCl 860C "/02 two directions crossed relative to the mid-circumferential[58] Fieid 359 plane at angles ranging from 10 to 65. The latter layersare 1 61/47 disposed radially inwardly relative to the armor. A thirdlayer I of extensible metal cords is positioned radially outwardly of[56] References Cited the armor, the cords ofsuch layer being inclinedwith respect 7 I I v to the mid-circumferential plane at an angleranging between UNITED STATES PATENTS and 1 3,557,858 1/1971 8 Claims, 2Drawing Figures PATENTEDJUH 6 I972 3,667, 527' 5 INVENTORS f5 CARLOMAGISTRINI LUIGI MAIOCCHI 6M5, @w's m %o m ATTORNEYI TREAD RING FORREMOVABLE TREAD TIRES The present invention concerns removable treadtires; namely, pneumatic tires in which the anchorage of the tread tothe carcass is obtained by means of the friction forces produced byinflation of the tire.

The related prior art, including several patents of the applicant,discloses that the tread ring is provided with an assembly ofreinforcing structures, whose arrangement has a critical influence ontire performance, in particular in respect to road holding, steeringsafety and travelling comfort. More particularly, the tread ringcomprises a tension-resistant armor, constituted by a single metal cord,helically wound whose coils are disposed in a direction substantiallyparallel to the mid-circumferential plane of the tire. The armor servesto withstand the carcass expansion, in order to produce the frictionforces which provide the anchorage of the tread ring on the carcass.

However, the armor is not sufficient by itself to impart to the tire themany features required for good performance during use.

It is known that, in the tire field, the problems of a complexreinforcing structure are generally solved by the adoption of anassembly formed by three layers, the respective elements of which aredisposed along different directions in the various layers. It was foundthat, by providing two strips of metallic fabric in a radially outermostposition with respect to the above indicated armor, and by arrangingthem so that their cords are symmetrically inclined with respect to themid-circumferential plane of the tire, it is possible to distribute overa wide portion of the tread stresses caused by a small obstacle, andmoreover to improve the transversal or torsional rigidity of the treadring, affecting in a positive manner the drift characteristics of thetire and its road holding ability.

However, it was also found that the above described reinforcing assemblydoes not completely solve other needs, which are necessary for good tireperformance, for instance, in particularly difficult conditions, as onbad ground. Actually, in such an assembly, the helical winding can beprotected towards the tire outside, but is not sufficiently protectedtowards the tire inside. Especially because of the impacts of the treadagainst possible obstacles, the reinforcing assembly reacts at theimpact point, taking although temporarily a convexity directed towardsthe tire inside, with a consequent thinning out of the coils forming thearmor in the concerned zone. This results in damage to the rubber layerunderlying the armor and, in the course of time, a weakening of thehelically wound cord. Consequently, besides the disruption of the armorof the tread ring, the cord pieces damage the carcass, thus reducing theservice life of the tire.

Attempts were made to prevent the above indicated disadvantages byplacing one of the two strips of metal cords superimposed to the armorbelow the latter. In this way the reinforcing assembly shows the twostrips having their cords symmetrically inclined with respect to themid-circumferential direction to maintain the good characteristics oftransversal rigidity and of drift of the tire, while the existence ofthe strip below the armor ensures its integrity even in serious serviceconditions.

Also, this structure, however, does not constitute the complete solutionof all the problems involved in obtaining good performance of the tire.In fact, even if it represents a good level compromise, it involves adeleterious effect on the transversal or torsional resistance of thetread ring, in particular when the tire has to run on bad ground.

Obviously, a reinforcing assembly made of three layers, substantiallyconstituted by an armor whose coils are parallel to themid-circumferential direction of the tire and by two strips of cordfabric whose cords are symmetrically inclined, can be prepared accordingto a third arrangement; namely, by disposing both of said strips belowthe armor.

However, tests carried out by the applicant in this respect did not leadto such results as to perrrrit an evaluation of the validity and of theadvantages of this solution in comparison with the others, since it wasnoted that the reinforcing assembly so prepared involves an inadmissiblesensitivity of the tire to the so-called ridge effect". This latterexpression means the difficulty of mastering the vehicle when, inexceptional driving conditions, it travels with its near-side wheels onthe road edge, where there is a difierence in height between the vergeand the asphalt paved road. In such conditions the tire shows a tendencyto come down to the verge and to go forward on the road in a diflicultto control manner.

The applicant unexpectedly found a reinforcing asembly by means of whichit is possible to obtain a tread ring for removable tread tires whichgives the tire a service performance to well satisfy the above indicatedrequirements.

Briefly summarized, the present invention is a tread ring for pneumatictires separable from the carcass, which comprises an armor resistant totension in a longitudinal direction, formed by a helically wound metalcord, whose coils are disposed in a direction substantially parallel tothe mid-circumferential plane of the tire, and has two additional layersof metal cords, parallel to one another in each layer and disposed alongtwo directions crossed with respect to said mid-circumferential planeand forming with the latter angles ranging from 10 to 65, and which ischaracterized in that the additional layers are each disposed in aradially innermost position with respect to the armor, and in that saidtread ring has a third additional layer of extensible metal cordsdisposed in a radially outermost position with respect to said armor andinclined with respect to the mid-circumferential plane of the tire at anangle ranging between 10 and 65.

The expression extensible metal cords" means in the presentspecification those cords which, when they are rubberized, possess anapparent modulus of elasticity, for loads smaller than one-tenth of theultimate tensile stress, not higher than 3,500 Kglmm The metal cordsconstituting the third additional layer, external to the armor, may beextensible because of their particular structure. Cords of this kindare, for example, those whose elements are all twisted in the samedirection and there is not a central core, namely, the twisting sense ofthe strands is the same as that of the cord. According to a preferredembodiment, the cords constituting the three additional layers areinclined, with respect to the mid-circumferential plane of the tire, atan angle ranging from 10 to 30. This embodiment adds to the tire life,and is therefore intended in particular for those cases in which themain problem is tire mileage.

In a further preferred embodiment of the invention, the externaladditional layer is disposed so that its cords are inclined, withrespect to the mid-circumferential plane of the tire, in the samedirection as the cords of the internal additional layer closer to thearmor.

The width of the additional layers, internal to the armor, must be atleast equal to the width of the armor. However, the external additionallayer may have a width less than 40 percent of the width of the armor.

It has been ascertained that the presence of a third additional layerdisposed externally to the armor has a determinant influence on thebehavior of the tread ring, cooperating in an efficient manner with theother layers forming the above described reinforcing assembly. In fact,a pneumatic tire provided with such a tread ring has excellentcharacteristics of driving safety, road holding and travelling comfort,without affecting the desired tire performance.

The present invention may now be better understood by reference to theaccompanying drawings, given by way of nonlimiting example, in which:

FIG. 1 represents partially and in section a pneumatic tire according tothe present invention; and

FIG. 2 represents, in plane development, the tread ring of FIG. 1, withparts broken away to show the arrangement of the cords inside the tread.

FIG. 1 represents a 12.00 R 20 size removable tread tire consisting of atread ring 1 and of a carrying casing 2. The tread ring 1 is inwardlyprovided with an armor 3, constituted by a helically wound metal cordforming a single layer, the

coils of said cord being disposed (see FIG. 2) in a directionsubstantially parallel to the mid-circumferential plane. The used cordcan have a 7(7 3 )/O. 15 structure and a diameter of 2.70 mm, theexpression 7(7 3)/0.l5 meaning in this case a cord formed by the unionof seven cords, each formed by seven strands of three wires each. Eachwire has a diameter of 0.15 mm.

The armor has a width L equal to 205 mm. Two additional layers 4 and 5are disposed in a radially innermost position with respect to the armor.These layers are both formed by metal cords parallel to one another, andsymmetrically inclined, with respect to the mid-circumferential plane,by angles a and B, respectively, having a value of 20. The additionallayers have a width L of 210 mm; namely, a width slightly exceeding thatof armor 3.

A further additional layer 6, also formed by metal cords parallel to oneanother, is provided in a radially outermost position with respect toarmor 3. This layer is also formed by metal cords parallel to oneanother, which form with respect to the longitudinal direction an angle'y equal to 20", having the same sign as the angle a. The additionallayer 6 has a width L corresponding to about 80 percent of the width Lof the armor 3, and corresponding therefore to 165 mm.

The cords of the additional layers 4- and 5 have a 7X3/0. 15 structureand a diameter of 0.90 mm, the expression 7 3/0. l5 meaning in this casea cord formed by seven strands of three wires each; each wire has adiameter of 0. 15 mm. The cords of the layer 6 have a 3X7/O. 175structure (three strands of seven wires each) and are formed, aspreviously stated, by adopting the same twisting sense both for theseven elements and for the cord. Their diameter is 1.10 mm. These cordshave an apparent modulus of elasticity, for loads smaller than one-tenthof the ultimate tensile stress, equal to 2,200 Kglmm It should beunderstood that the above described embodiment is of a non-limitingcharacter, and that the present invention includes any alternativeembodiment deriving from the inventive concept involved.

What is claimed as new is:

1. A tread ring for a pneumatic tire of the type in which the tread isseparate from the carcass, which comprises an armor resistant to tensionin a longitudinal direction, formed by a helically wound metal cordwhose coils are disposed in a direction substantially parallel to themid-circumferential plane of the tire and moreover comprises twoadditional layers of metal cords parallel to one another in each layerand disposed along two directions crossed with respect to saidmid-circumferential plane, and forming with the latter angles rangingfrom 10 to 65 and is characterized in that said two additional layersare both disposed in a radially innermost position with respect to saidarmor, and in that said tread ring comprises a third additional layer ofextensible metal cords, disposed in a radially outermost position withrespect to said armor and inclined with respect to themid-circumferential plane of the tire at an angle ranging between 10 and65, the cords of said third layer being extensible relative to the othermentioned cords in that said third layer cords have an apparent modulusof elasticity not exceeding 3,500 Kg per mm at loads smaller thanone-tenth of the cord ultimate stress.

2. A tread ring as in claim 1, characterized in that the cords of theadditional layers are inclined, with respect to the midcircumferentialplane of the tire, at an angle ranging between 10 and 30.

3. A tread ring as in claim 1, characterized in that the additionallayer external to the armor has a width not greater than the width ofsaid armor itself, but not less than 40 percent the width of the armor.

4. A tread ring as in claim 3, characterized in that the additionallayer external to the armor is constituted by metal cords whose elementshave the same twisting direction.

5. A tread ring as in claim 1, characterized in that the angle ofinclination of the cords of the additional layer external to the armoris of the same sign as the angle of inclination of the cords of theinner additional layer closer to the armor.

6. A separable tread ring for pneumatic tires embodying an armorlongitudinally resistant to tension, at least two layers of metal cordsdisposed parallel to each other in each layer and crossed in oppositedirections relative to the mid-circumferential plane of the tire atangles ranging between 10 and 65, said last named layers beingpositioned radially inwardly of said armor, and an additional layer ofmetal cords disposed radially outwardly of said armor, the cords of saidlast recited layer being inclined at an angle ranging between 10 and 65with respect to said mid-circumferential plane, the last recited cordsbeing extensible relative to the cords of said two layers in that theyhave an apparent modulus of elasticity not exceeding 3,500 Kg per mm atloads smaller than one-tenth of the cord ultimate stress.

7. The tread ring defined by claim 6, said armor being formed by metalcords, the coils of which are disposed generally parallel to themid-circumferential plane of the tire.

8. The tread ring of claim 1, said third layer cords having aconsiderably greater extensibility than the other mentioned cords byvirtue of their being formed of wires wound in the same direction andwithout the presence of a central core element within the wound wires.

1. A tread ring for a pneumatic tire of the type in which the tread isseparate from the carcass, which comprises an armor resistant to tensionin a longitudinal direction, formed by a helically wound metal cordwhose coils are disposed in a direction substantially parallel to themid-circumferential plane of the tire and moreover comprises twoadditional layers of metal cords parallel to one another in each layerand disposed along two directions crossed with respect to saidmid-circumferential plane, and forming with the latter angles rangingfrom 10* to 65* and is characterized in that said two additional layersare both disposed in a radially innermost position with respect to saidarmor, and in that said tread ring comprises a third additional layer ofextensible metal cords, disposed in a radially outermost position withrespect to said armor and inclined with respect to themid-circumferential plane of the tire at an angle ranging between 10*and 65*, the cords of said third layer being extensible relative to theother mentioned cords in that said third layer cords have an apparentmodulus of elasticity not exceeding 3,500 Kg per mm2 at loads smallerthan one-tenth of the cord ultimate stress.
 2. A tread ring as in claim1, characterized in that the cords of the additional layers areinclined, with respect to the mid-circumferential plane of the tire, atan angle ranging between 10* and 30*.
 3. A tread ring as in claim 1,characterized in that the additional layer external to the armor has awidth not greater than the width of said armor itself, but not less than40 percent the width of the armor.
 4. A tread ring as in claim 3,characterized in that the additional layer external to the armor isconstituted by metal cords whose elements have the same twistingdirection.
 5. A tread ring as in claim 1, characterized in that theangle of inclination of the cords of the additional layer external tothe armor is of the same sign as the angle of inclination of the cordsof the inner additional layer closer to the armor.
 6. A separable treadring for pneumatic tires embodying an armor longitudinally resistant totension, at least two layers of metal cords disposed parallel to eachother in each layer and crossed in opposite directions relative to themid-circumferential plane of the tire at angles ranging between 10* and65*, said last named layers being positioned radially inwardly of saidarmor, and an additional layer of metal cords disposed radiallyoutwardly of said armor, the cords of said last recited layer beinginclined at an angle ranging between 10* and 65* with respect to saidmid-circumferential plane, the last recited cords being extensiblerelative to the cords of said two layers in that they have an apparentmodulus of elasticity not exceeding 3,500 Kg per mm2 at loads smallerthan one-tenth of the cord ultimate stress.
 7. The tread ring defined byclaim 6, said armor being formed by metal cords, the coils of which aredisposed generally parallel to the mid-circumferential plane of thetire.
 8. The tread ring of claim 1, said third layer cords having aconsiderably greater extensibility than the other mentioned cords byvirtue of their being formed of wires wound in the same direction andwithout the presence of a central core element within the wound wires.